The present invention relates to semiconductor devices and, more particularly, to an integrated circuit including copper interconnections.
Semiconductor devices in the form of integrated circuits are widely used in many electronic devices. A typical integrated circuit includes a substrate, active regions formed in the substrate, and one or more conductive interconnection layers on the substrate. Each interconnection layer typically includes a plurality of closely spaced metal or conductive lines. These conductive lines connect active portions on the substrate, and provide for external connections to the active circuit portions.
Dielectric layers, also known as inter-level dielectric (ILD) layers, typically formed of silicon dioxide, separate adjacent interconnection layers. The metal lines of vertically spaced interconnection layers may be connected by vertically extending vias.
Increasing performance demands for integrated circuits have resulted in greater circuit densities. Accordingly, device sizes are being continually reduced. Reduced signal propagation delays are also desired. The cross-sectional area of interconnections has been decreased as circuit densities increase. Unfortunately, an increase in the interconnection resistance and stray capacitance degrades signal propagation speed.
A number of interconnection materials have been used including polysilicon and aluminum, for example. For increased conductivity, silicided polysilicon, aluminum, and tungsten are also now more commonly used for the interconnections. Large current densities in small cross-sectional aluminum interconnections, for example, may lead to electromigration, and voiding. Aluminum has been alloyed with small proportions of copper to enhance electromigration resistance. Tungsten, for example, has good electromigration resistance, but has a relatively high electrical resistance. Copper, in comparison, has both good electromigration resistance and a relatively low electrical resistivity of about 1.7 xcexcohmxc2x7cm. Unfortunately, copper is relatively quick to oxidize especially during processing or manufacturing of the integrated circuit.
Passivation techniques have been attempted to reduce or prevent the oxidation of the upper surface of copper interconnections. Silicon dioxide has been used as the passivating layer, but has a tendency to oxidize the copper. An alternate approach is to form a silicon nitride passivating layer on the exposed upper surface of the copper during manufacturing. Yet another approach is to form a phosphosilicate glass passivation layer on the copper interconnection.
Existing passivating techniques may be unsatisfactory. In addition, the passivating layers, such as silicon nitride or phosphosilicate glass may have relatively high dielectric constants. These high dielectric constants cause increased signal propagation delays.
In view of the foregoing background, it is therefore an object of the invention to provide an integrated circuit and associated manufacturing methods including copper interconnections with an effective passivation thereon.
It is another object of the invention to provide an integrated circuit and associated methods including copper interconnections and with an adjacent dielectric layer with a relatively low dielectric constant.
These and other objects, features and advantages in accordance with the present invention are provided by an integrated circuit which in one embodiment comprises a substrate, at least one interconnection layer adjacent the substrate and comprising copper lines, and wherein each of the copper lines comprises at least an upper surface portion including at least one copper fluoride compound. The at least one copper fluoride compound preferably comprises at least one of cuprous fluoride and cupric fluoride. The compounds of copper and fluoride are relatively stable and provide a reliable and long term passivation for the underlying copper.
The integrated circuit may also preferably include a dielectric material on the upper surface portion of the interconnection layer. In accordance with one particularly advantageous embodiment of the invention, the dielectric material may comprise fluorosilicate glass (FSG). During formation of the FSG layer in accordance with one embodiment of the invention, the upper surface of the copper reacts with the fluorine to form the desired stable copper fluoride compound(s) which then acts as a passivation layer for the underlying copper. In accordance with another embodiment, the surface of the copper line is prefluorinated so as to prevent depletion of the fluorine from the FSG layer.
In yet other embodiments, the dielectric material may comprise an oxide, such as silicon dioxide, for example. In yet another embodiment, the dielectric material comprises air.
For a typical integrated circuit, the upper surface portion of the copper line may have a thickness in a range of about 2 nm to 20 nm. In addition, the copper line may have an overall thickness in a range of about 300 nm to 500 nm. Accordingly, the upper copper fluoride portion, which has a higher electrical resistivity than the underlying copper, is only a small percentage of the overall line. This percentage may be less than about 10%, for example.